1. Field of the Invention
The present invention relates to temperature compensation of a tuner, and more particularly, to a tuner in which Take-Over Point (TOP) is compensated for according to a temperature.
2. Background of the Related Art
FIG. 1 shows the construction of a tuner according to the related art.
FIG. Shows a tuner (receiver) 1 according to the related art.
After a received signal passes through an antenna 2, a bandpass filter 3 located at the front end of a first (variable) amplification stage 4 selects a desired frequency band (e.g., WCDMA/GSM, etc.).
The bandpass filter 3 can be a part of a dual filter shape such as duplexer mode including a transmission-side bandpass filter.
A mixer 5 down-converts the filtered signal into a zero Intermediate Frequency (IF) by using an orthogonal local oscillator signal (6) (whose phase is shifted by 90 degrees), which is tuned by a RX synthesizer 7 of a carrier frequency of a received channel.
The down-converted signal is adapted to bandpass filters 8, 10 and a filter 9. In a digital communication system, this information is converted into digital form by an A/D converter 11 and is then digitally filtered (12).
Channel decoding (13) and other digital functions necessary to recover received information are performed after the operation by the A/D converter (11).
A gain control function is an important function in that a range of an input signal is extended such that it can be used in all kinds of tuners. A signal of a Received Signal Strength Indicator (RSSI) block 14 is supplied to a gain control logic block 15 that maintains a received signal to a desired level by controlling the gains of the amplifiers 4, 8 and 10.
In the conventional tuner, however, a Radio Frequency (RF) gain can be kept constant by the gain control unit and the RSSI. A TOP in which a RF gain falls depending on variation in temperature outside the tuner is varied. Due to this, a problem arises because a signal to noise (S/N) ratio is not kept constant.